Unbound Local Error：在try和except语句内进行赋值之前引用的局部变量

Question

I am attempting to create a very simple menu system, using all of the pythonic tools, (try and except statements, loops, if statements) and I have run into a little bit of trouble.

This is the code and error message i have at the moment

def Menu():
while True:
    print("""
    Hello, please enter a number 1 - 4
        1 - Compliment
        2 - Fact
        3 - Insult
        4 - Quit
        """)

    try:
        UserInput_INT = int(input("> "))


    except ValueError:
        UserInput_STR = (UserInput_INT)
        if len(UserInput_STR) == 0:
            print("You have entered nothing. Please enter a number between 1 and 4")
        print("You entered a character. Please enter a number between 1 and 4")
        Menu()

    if  UserInput_INT not in range (1, 5):
        print("Invalid input please enter a whole number between 1 and 4")
        continue

    UserInput_STR = (str(UserInput_INT))
    if UserInput_STR == '1':
        print(" You look horrible today!")

    elif UserInput_STR == '2':
        print("Sam Birkenshaw & Jordan Ives can code better than Mr Bath. ")

    elif UserInput_STR == '3':
        print("You are bad at coding ")

    elif UserInput_STR == '4':
        quit()

Menu()

error message:

"Traceback (most recent call last): File "E:/All/School Work/Computer Science/Code/SAM broken code.py", line 12, in Menu UserInput_INT = int(input("> ")) ValueError: invalid literal for int() with base 10: ''

During handling of the above exception, another exception occurred:

Traceback (most recent call last): File "E:/All/School Work/Computer Science/Code/SAM broken code.py", line 39, in Menu() File "E:/All/School Work/Computer Science/Code/SAM broken code.py", line 16, in Menu UserInput_STR = (UserInput_INT) UnboundLocalError: local variable 'UserInput_INT' referenced before assignment"

I need to have it so that if the user enters nothing, there is a different message displayed than if they enter a letter, and if they enter something other than one of the accepted answers.

(I am runing python 3.6.2 currently)

Answer 1

The value that is being passed as input to the program is not a valid integer. Now, when an exception is raised the variable UserInput_INT is not being assigned causing the second error. Try checking if the value is integer before trying to cast it.

input = input("> ")
UserInput_INT = int(input) if input.isdigit() else input

As a side note, please try to follow naming conventions.